After energy-saving optimization of turbine governing valve of a 1 000 MW unit, more than 40 low-frequency oscillation cases have occurred within a year with unknown reasons, where the amplitudes were from 10 to 30 MW, the oscillation period were from 4 to 27 seconds, and the duration time were from a few seconds to tens of minutes. By analyzing the logic circuits of coordinated control system (CCS) of the unit and by carrying out corresponding modeling and simulation, it is confirmed that the causes of power oscillation include improper parameter settings of the macro-filtering module for power signal in CCS, too large parameter setting of control ratio in the CCS power controller, and improper computing sequence of logic configuration in distributed control system (DCS), while the inducement factor is that the gradient of valve flow characteristics is too large after turbine governing valve being optimized. By tuning the parameters of the macro-filtering module of CCS power signal and that of the power controller, and by reconfiguring the computing sequence of logic group in DCS, the phenomenon of low-frequency power oscillation is eliminated.